Suspensions Flashcards

1
Q

What is a suspension?

A

suspensions are dispersions in which insoluble drug particles (solid) are suspended in liquid vehicle (external phase)

disperse phase - insoluble solids
continuous phase - liquid medium

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2
Q

Why are suspensions used?

A

used for insoluble or poorly soluble drug
- volume of liquid required to dissolve the drug is too large

used due to the instability of some drugs in water

  • preparation immediately before use
  • limited shelf-life
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3
Q

What are the advantages of suspensions?

A

mask the taste of therapeutic agents
patients who have difficulty swallowing solid dosage forms
provide controlled drug delivery (intramuscular injections)

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4
Q

What are the characterises of a stable suspension?

A

good wettability

  • depends on the contact angle
  • required wetting agents

sedimentation velocity

  • stoke’s law
  • particle size = smaller is better
  • viscosity of continuous phase (vehicle) = higher is better

sediment re-dispersibility

  • depends on flocculated and deflocculated systems
  • require flocculating agents
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5
Q

How does powder wettability affect suspension stability?

A

determined by measuring the contact angle = between the water droplets and the powder

smaller contact angle is required = hydrophilic

  • good spreadability
  • easy dispersing

interfacial tension

  • between liquid and solid
  • must be reduced as it pulls sphere inward creating a more spherical shape
  • require a less spherical shape

surface tension

  • liquid and gas= must be reduced to create a less spherical shape
  • solid and gas = not affected, pushes surface outwards
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6
Q

What are examples of wetting agents?

A

hydrophilic polymers
- cellulose
- acacia
increases viscosity of the continuous phase

co-solvents can be used to enhance solid wettabilty

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7
Q

How can rate of sedimentation be controlled? Why must it be controlled?

A

stoke’s law

  • reduce particle size = less irritation, ease of administration, no coalesce
  • increase viscosity of the continuous phase (vehicle) = prevents/slows movement of disperse phase, hydrophilic polymers, polysaccharides
  • reduce density difference

must remain stable to get consistent uniform doses
- prevent overdose and underdose

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8
Q

How can sediment re-dispersibilty affect stability of suspension? What system is required?

A

aggregated clusters that form as the suspension sits must be re-dispersed to get a uniform dosage

deflocculated

  • low sedimentation
  • low volume
  • sediment contains few voids
  • sediment is difficult to redisperse

flocculated

  • high sedimentation
  • high volume
  • sediment contains many voids
  • sediment can be re-dispersed
  • no caking
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9
Q

What are the possible interactions for control flocculation?

A

no interaction = slow individual sedimentation

repulsion > attraction = slow individual sedimentation, compact sediment

attraction > repulsion = irreversible interaction, coagulation

balanced attractive-repulsive forces - loose interaction, loos floccules/aggregates produced , re-dispersible sediment

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10
Q

What are flocculating agents?

A

electrolytes
surfactants
polymers
- starch

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